The invention relates to an arrangement for pulse-width modulating an input signal said arrangement comprising a pulse-width modulator and pre-compensation means connected in the input lead to the pulse-width modulator to pre-compensate for non-linear errors of said pulse-width modulator. Such arrangement is known from the article “Dynamic Model-Based Linearization of Quantized Pulse-Width Modulation for Applications in Digital-to-Analog Conversion and Digital Power Amplifier Systems” by M. O. J. Hawksford, Journal of Audio Engineering Society, Vol. 40, April 1992, pp. 235-252.
This arrangement may e.g. be used for driving class D audio power amplifiers. The class D technology enables high power audio amplifiers that are small enough to design stylish multi-channel audio systems. The input signal is delivered to the pulse-width modulator where the signal is converted into a two level pulse-width modulated signal (with levels 0 and 1) or a three level pulse-width modulated signal (with levels −1, 0 and +1) with a switching frequency that is substantially higher than the highest audio frequency. The pulse-width modulated signal may drive C-MOS switches that in turn drive a loudspeaker through an LC filter for substantially removing the high switching-frequency signal components from the loudspeaker. The class D amplifier has high power-efficiency because the power losses in the switches and in the LC-filter are relatively small.
A problem however is that pulse-width modulation is inherently a non linear operation especially for higher modulation indices, with the result that the pulse-width modulated output signal is subjected to non linear distortion. This non-linearity is caused by the fact that the frequency spectrum of each individual pulse is dynamically modified as a function of the pulse-width. The subsequent summation over all pulses results in a dynamic spectral modulation that is the root of the non-linearity. The above-identified article seeks to pre-compensate the non-linear distortion of the pulse-width modulator by subjecting the input data of the pulse-width modulator to finite impulse response filters whose coefficients shift with the input data. This results in a very complex realization and a reduction of the non-linear distortion by only about 10 dB.